Control circuit



w. KLEIN CONTROL CIRCUIT DMn s, 1960 4 Sheets-Sheet. 1

Filed Nov. 7, 1958 lila l Dec. 6, 1960 Filed NOV. 7. 1958 COLLECTOR VOLTAGE w. KLEIN 2,963,293

CONTROL CIRCUIT 4 Sheets-Sheet v 2 INVENTOR WALTER KLEIN BY mi@ Wmm HIS ATTORNEYS COLLEGTOR CURRENT-( A Dec. 6, 1960 Filed Nov.

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W. KLEIN CONTROL CIRCUIT INVENTOR WALTER KLEIN BY 4m d K@ www HIS ATTORNEYS Dec. 6, 1960 E w. KLEIN 2,963,293

CONTROL CIRCUIT Filed Nov. '7, 1958 4 Sheets-Sheet 4 9 o NM-1w sa KHG-HHH 8 (I) r O N Fm" mvENToR o 9 O WALTER KLEIN BY /Qw/ (D WM ,MMM

HIS ATTORNEYS United States PatentO Cash Register Company, Dayton, Ohio, a corporation of Maryland Filed Nov. 7, 1958, Ser. No. 772,624

8 Claims. (Cl. 271-57) This invention relates generally to control circuits and, more particularly, to control circuits employing photosensitive elements utilized with apparatus operable with substantially opaque items.

The present invention is designed to operate with highspeed sorting apparatus, such, for instance, as that disclosed in co-pending application for United States Letters Patent, Serial No. 731,405, tiled on April 28, 1958, in the name of Allen W. Daubendiclc The sorting apparatus includes a transport means defining a path of travel for items, such as bank checks bearing various data thereon, and a feed means for feeding individual itemsV to the transport means. The feed means is designed to feed a certain number of items onto the transport means per minute in such a manner that a predetermined spacing exists between the items. The transport means is normally operableto maintain this predetermined spacing between items to insure that the items are in correct position when appropriate sorting pockets in the sorting appal r-atus are conditioned to receive them. Such sorting apparatus is designed to sort items yat a rate of between 700 and 800 items 'a minute.

At such high speed of operation, there may occur times when the predetermined spacing between items is not effected by the feed means, or it is not maintained by the transport means. At such times, it is -advantageous that the feed means and the transport means be made inoperative to prevent the sorting apparatus from performing erroneous sorting operations, and also to prevent damage from being done to the sorting apparatus.

Accordingly, an object of the present invention is to provide a control circuit employing photosensitive elements for utilization with apparatus operable with substantially opaque items, which items are adapted to travel in a predetermined spaced order in such apparatus.

Another object is to provide a control circuit employing photosensitive elements .to control travel of the items in such an apparatus.

A further object is to provide a control circuit employing photosensitive elements, and operable in synchronism with feeding of the items, lfor controlling travel of the items in such an apparatus.

A still `further object is to provide a control circuit employing photosensitive elements, and operable in synchronism with feeding of the items in such an apparatus, for controlling the feeding of the items.

Still further objects of the present invention will become apparent during the following description of the apparatus.

Broadly, the present invention comprises a control circuit for use with apparatus operable with substantially opaque items. The control circuit includes a plurality of serially-connected photosensitive devices, which are positioned at predetermined points adjacent to a transport means. The transport means deiines a path of travel for the items. In the particular embodiment to be described in detail hereinafter, the photosensitive devices are phototransistors, although other photosensitive devices, such as y mechanism 10.

phototubes, may be used. A means for applying light to the photosensitive devices is also provided. The lightapplying means includes a light source for each of the photosensitive devices positioned adjacent to the other side of the path of travel.

The apparatus utilizing the control circuit includes a feed means, for feeding the items to the transport means at spaced intervals, and a timing means. The timing means is associated with the feed means and operates to develop timing signals which occur in synchronism with operation of the feed means.

The photosensitive devices of the control circuit are operable to'effect control of the feed means when an item is adjacent to at least one of the predetermined points, where a photosensitive device is positioned, at a time a timing signal occurs.

More specifically, the present invention further includes means operable to prevent the feed means from feeding items to the transport means, and a gating circuit for passing certain of the timing signals to the feed preventing means to control the operation thereof. A current-responsive means is provided, which is responsive to current ow through the serially-connected photosensitive devices, to control operation of the gating circuit.

A more complete understanding may be had of the invention when the following detailed description thereof is read in conjunction with the accompanying drawings, wherein like reference characters refer to like or similar parts, and in which:

Figure l is a diagram showing in block form the control circuit for controlling the travel of items in a sorting apparatus; f

Figures 2(A) to 2(D), inclusive, illustrate characteristics of the photosensitive elements of the control circuit of Figure l during various conditions of operation;

Figures 3(A) to 3(D), inclusive, illustrate the manner whereby the control circuit is made to operate in synchronism with the feeding of items; and

Figure 4 illustrates schematically a control circuit embodying principles of the present invention.

At the outset of the description, it should be noted that the instant invention is being described as operating in conjunction with the sorting apparatus disclosed in the above-mentioned patent application of Daubendick. Accordingly, only as much of the sorting apparatus will be disclosed in this application as will permit a complete understanding of the invention.

Referring now to Figure l, there is shown a feed mechanism 10 for feeding opaque items, such as those shown at 1.1 and 12, to a transport means 14, which defines a path of travel for the items.

The feed mechanism 10 includes a suitable rotary mechanism, which operates to introduce one item at a time and two items for every revolution of the rotary mechanism to the transport means 14.

A signal generator 16 is associated with the feed The signal generator 16 includes another suitable rotary mechanism connected so as to rotate in synchronism with the rotary mechanism of the feed mechanism 10. This latter rotary mechanism is provided with two magnetic elements situated in different positions on its surface. Two lstationary field windings are provided, in each of which a signal is developed when the magnetic element of thelatter rotary mechanism enters its field. The field windings are positioned with respect tothe position of 'the magnetic elements on the rotary mechanism so that a timing signal is generated at the time an item is fed to the transport means 14.

Photosensitive devices 18 and 20 are positioned adjacent to one side of the transport means 14 at predetermined points. Light sources 22 and 24 are disposed adjacent to the other side of the transport means 14, so

as to emit light on the photosensitive surfaces of the photosensitive devices.

In the arrangement shown in Figure 1, the photosensitive device 18 and its associated light source 22 are positioned in alinernent with a sensing device 26, which is utilized to sense the information carried -by the items as they pass by it, while the photosensitive device 20 and its associated light source 24 are positioned in alinement with a pocket control device or gate 28, which operates to direct an item into its associated pocket 30 when it is made operable. The control device 28 is made operable upon analysis of the information carried by an item. The sorting apparatus has a photosensitive device and a light source simil-arly positioned with respect to its remaining pocket control devices.

For operating the feed mechanism 10, the signal generator 16, and the transport means 14, power from a power source 32 is supplied over a path including leads 34 and 35, and switch elements 36 and 37. The actuation of a push-button switch 38 energizes a relay 40, which operates to close the normally open switch elements 36 and 37. A normally closed switch element 42 is connected in series with the push-button switch 38 and the relay 48. The switch element 42, when opened, deenergizes the relay 40 and opens the switch elements 36 and 37, thus preventing operation of the feed mechanism 10, the signal generator 16, and the transport means 14.

The photosensitive devices 18 and 2t) are coupled through an amplifier or current-responsive means 44 to a gating circuit 46, which also is coupled to the signal generator 16. The gating circuit 46 is coupled through a monostable or one-shot multivibrator 48, a driver 50, and `a -power amplifier 52 to a relay 54. The relay 54, When energized by the power amplier 52, operates to open the switch element 42, which in turn causes deenergization of the relay 4t), thus opening the switch elements 36 and 37. The feed mechanism 10 and the transport means 14 will in this case cease to function.

An embodiment of the control circuit of the present invention is shown in Figure 4, described hereinafter. Phototransistors are utilized in Figure 4 for the photosensitive devices 18 and 20 of Figure 1. Figure 2(A) illustrates the collector current versus collector voltage characteristics for the phototransistors. Curve 56 represents generally the dark current characteristic of each of the phototransistors when light from the light sources 22 and 24 is not applied to their photosensitive surfaces. Curve 58 represents generally the characteristic of each of the phototransistors when light from the light sources 22 and 24 is applied to their photosensitive surfaces. Curves 60 and 62 in Figure 2(B) represent the characteristics of the phototransistors in the case where both of the phototransistors have light applied to them from their associated light sources. The curves 60 and 62 are shown as differing somewhat, since the response of the vphototransistors may not be exactly the same. Curve 64 represents the composite characteristic for both of the phototransistors when light is applied to them. It will be noted that the composite curve 64 is slightly less than the curve 62. Curves 66 and 68 in Figure 2(C) represent the characteristics of the phototransistors in the case where an item prevents light from the light sources from being applied to them. Curve 70 represents the composite characteristic for the phototransistors in this case. In Figure 2(D), curve 72 represents the characteristic of a phototransistor when light is applied to it, while curve 74 represents the characteristic of the other phototransistor when an item prevents light from being applied to it from its associated light source. In this case, the composite characteristic is represented by curve 76, which shows a response slightly less than that represented by the curve 74.

The arrangement described in Figure 1 operates in the following manner: When the push-button switch 38 is actuated, -power from the power source 32 is applied to the feed mechanism 10, causing the feeding of items to the transport means 14. The items will travel along the transport means in a patch adjacent the light sources 22 and 24 and the various pocket gates, such as 28, of the sorting apparatus.

At the time of feeding of an item to the transport mechanism 14, a timing signal such as that shown at 78 is developed by the signal generator 16. The timing signals are applied to one input of the gating circuit 46. The gating circuit 46 is operative to pass timing signals from the signal generator 16 through pulse-forming and amplifying circuits, including the multivibrator 48, the driver 50, and the power amplifier 52, to the relay 54 to energize it when an inhibiting control voltage present at another input of the gating circuit 46 is removed.

An item will be correctly located on the transport means 14 if, at the time of occurrence of a timing signal, it is not adjacent to the predetermined points where the photosensitive devices are located. If the items are correctly located on the transport means 14, light from the light from the light sources 22 and 24 will be applied to the photosensitive devices, causing them to conduct and present a first or large current to the input of the current-responsive means 44. The current-responsive means 44 will have no effect on the inhibiting control voltage normally present at one of the inputs of the gating circuit 46. Thus, a timing signal will not be passed by the gating circuit 46 to effect operation of the relay 54 at that time.

But if an item is incorrectly located on the transport means 14 at the time of occurrence of a timing signal 78, this item will prevent light from a light source from reaching its associated photosensitive device. The pertinent photosensitive device will not conduct heavily, and a second or small current will be presented at the input of the current-responsive means 44. The current-responsive means 44, in response to this small current, will remove the inhibiting control voltage normally present at one of the inputs of the gating circuit 46. Thus, a timing signal will pass through the gating circuit 46 at this time and effect energization of the relay 54. Energization of the relay 54 will cause the feed mechanism 10 and the transport means 14 to cease their operation.

lIn Figure 3, Figure 3(B) shows a timing signal 78 occurring at a time designated as T1. This timing signal is developed as the first item 11 is fed to the transport means 14. There is also shown a timing signal 78, occurring at a later time designated as T2. This later-occurring timing signal is developed as the next or succeeding item 12 is fed to the transport means 14. Figure 3(A) shows that item 11 will be approaching the photosensitive device 18 at time T1 and will be approaching the photosensitive device 20 at time T2. The items 11 and 12 at the times T1 and T2, respectively, are shown correctly located along the transport means 14, so that they will not prevent light from being applied to the photosensitive devices 18 and 2t). In Figure 3(A), 11a represents an item which is incorrectly located on the transport means at the time of a timing pulse occurring at time T2. This incorrectly-located item 11a will prevent light from being applied to the photosensitive device 20. At 82 and 84 in Figures 3(C) and 3(D) there is represented the current owing through the photosensitive devices 18 and 20, respectively, at the time of a timing signal occurring at time T1, and at 86 and 88 there is represented the current flowing through the photosensitive devices 18 and 20 at the time of a timing signal occurring at time T2. At 90 there is represented the current flowing through the photosensitive device 20 at the time T2, when the item 11a of Figure 3(A) is incorrectly located on the transport means 14. In this case, the series current through the photosensitive devices 18 and 20 will be relatively small, as shown by the composite characteristic curve 76 of Figure 2(D).

Figure 4 is a schematic circuit diagram of the control circuit shown only in block form in Figure 1. Figure 4 shows phototransistors 92 and 94, each having at least an emitter electrode 96 and 98, respectively, and a collector electrode 100 and 102, respectively. The co1- lector electrode 100 of phototransistor 92 is connected in series with the emitter electrode 98 of phototransistor 94.

The emiter-collector paths of the phototransistors 92 and 94 are connected in series, preferably through a protective resistor 104 and a threshold control resistor 106, between ground 108 and the negative terminal of an operating potential source 110.

The light sources 22 and 24 (Figure l) are positioned to emit light on the sensitive surface of each of the phototransistors 92 and 94.

With this circuit, in the absence of light applied to the phototransistors 92 and 94, substantially no current will flow in the collector circuit of transistor 94 except that small amount represented by dark current ow. Hence, the impedance of the emitter-collector pathof the two phototransistors is very high, and substantially the entire voltage of the operating potential source 110 appears across the two phototransistors 92 and 94.

When light of sufficient intensity is applied from the light sources 22 and 24 to either of the phototransistors 92 or 94, the resistance of their emitter-collector paths is greatly reduced; but, when light is applied to only one of the phototransistors, the impedance of the emittercollector path of the other phototransistor remains sufficiently high to support substantialy the entire voltage of the operating potential source 110. Hence, current ow in the collector circuit of phototransistor` 94 is prevented except that represented by the dark current.

When, however, light is applied to both of the phototransistors 92 and 94, both of their emitter-collector paths become of low impedance, and a relatively large current starts to flow in the collector circuit of phototransistor 94. Under this condition, the voltages across the the phototransistors 92 and 94 are greatly reduced, and the voltage of the potential source 110 is concentrated to a large extent on the resistor 104.

The amplifier or current-responsive means 44 comprises the transistors 112 and 114. Each of the transistors 112 and 114 is connected in the common emitter configuration. Transistor 112 has a base electrode 116 connected to the collector electrode 102 of phototransistor 94, a collector electrode 118 connected through a resistor 120 to the potential source 110, and an emitter electrode 122 connected through a resistor 124 to the potential source 110 and also to the cathode 126 of a unilateral conducting device, such as a diode 128. The plate 130 of the diode 128 is connected to ground potential. Transistor 114 has a base electrode 132 connected through a coupling resistor 134 to the collector electrode 118 of transistor 112 and through a resistor 136 to ground potential, a collector electrode 138 connected through a resistor 140 to the potential source 110, and an emitter electrode 142 connected through a resistor 144 to the potential source 110 and to the cathode 146 of another unilateral connecting device, such as a diode 148. The plate 150 of the diode 148 is connected to ground potential.

The diode 128 and the resistor 124 represent a constant voltage supply for the emitter electrode 122 of transistor 112, which, in conjunction with the resistor 106, is utilized to hold transistor 112 in a cut-off state when a small current flows through the resistor 106. This small current is attributable to the dark current ow through the phototransistors 92 and 94. The magnitude of the darli current is dependent on temperature. Also, light leaking through an item incorrectly located on the transport means 14 may cause a small signal current to flow through the resistor 106. Therefore, before any current can ow in the collector circuit of transistor 94 through resistor 106, the voltage drop at resistor 106,' Aresulting from the current flow through the phototransistors 92 and 94, must be greater than the voltage across the diode 128. The resistor 144 and the diode 14-8 represent a constant voltage supply for the emitter electrode 142 of transistor 114, and they operate in the same manner for transistor 114 as the resistor 124 and the diode 128 do for transistor 112.

The voltage drop across the diode 148 and the base resistor 136 insures the complete cut-ott of transistor 114 even when the collector voltage of transistor 112 has not quite reached emitter potential.

Timing signals of positive amplitude are applied from the signal generator 16 (Figure l) through a coupling capacitor 152 to a gating circuit 154. The gating circuit 154 comprises a unilateral conducting device, such as a diode 156, and a resistor 158. The timing signals are applied to the plate 160 of the diode 156, at a time corresponding to the time of feeding of an item onto the transport means 14. The plate 160 of the diode 156 is connected through the resistor 158 to a point between the collector electrode 138 of transistor 114 and the resistor 140.

When light is applied to both of the phototransistors 92 and 94, a relatively large current will flow through the resistor 106, causing a voltage drop across it. This voltage drop will overcome the threshold voltage appearing across resistor 106, causing transistor 112 to conduct. With transistor 112 conducting, the voltage appearing at its collector electrode 118 will approach the voltage appearing at its emitter electrode 122. With transistor 112` fully conducting, the transistor 114 will be cut off, and substantially the voltage of the potential source will be applied to the plate 160 of the diode 156. This voltage will prevent the diode 156 from conducting and thus inhibit the passage of the timing signals through'the gating circuit 154.

When light is prevented from being applied to either of the phototransistors 92 or 94, the current through resistor 106 will decrease below the threshold current, causing transistor 112 to be cut off and driving transistor 114 into conduction. With transistor 114 conducting, the inhibiting voltage present in the plate 160 of the diode 156 will drop to substantially ground potential. The next timing signal will bias the diode 156 in the forward direction and will appear across the resistors 162 and 164, which are connected in series between the cathode 166 of the diode 156 and ground potential.

When transistor 114 is not conducting, the diode 156 will be biased in the reverse direction by the negative voltage appearing at its collector electrode 138, which voltage approaches the negative value of the voltage of the potential source 110. Thus, with transistor 114 nonconducting, the timing signals are prevented from passing through the gating circuit 154. In this circuit, the amplitude of the timing signals applied to the gating circuit 154 is smaller than the voltage of the potential source 110.

The timing signals appearing at the output of the gating circuit are utilized to energize the main power circuit breaker relay 54 if light from either of the light sources 22 or 24 is absent from either of the phototransistors 92 or 94 at the time a timing signal occurs. Since the timing pulses appearing at the output of the gating circuit 154 are of too short a duration andof too low power to effectively energize the relay 54, transistors 168, 170, and 172 and the power transistor 174 are provided for the purpose of wave-shaping and power amplitication of the timing signals.

The circuit including the transistors 168 and 170, the resistors 164, 176, 178, 180, 182, 184, and 186, and the capacitor 188 comprises a monostab'le multivibrator circuit in which the time constant is determined by resistor 176 and capacitor 188.

y The circuit comprising the transistor 172, along with coupling resistor 190 and current-limiting resistor 192, serves as a driver for the power transistor 174.

In the power amplifier circuit, unilateral conducting devices, such as the diodes 194 and 196, are connected in series with the resistor 198 to supply a cut-off bias to the transistors 172 and 174. Another unilateral conducting device, such as diode Ztiii, operates to short the transient voltage generated by the rapid rate of change of current through the inductance of the relay 54.

Normally, the transistor 16S is conducting. The .voltage on its collector electrode is close to ground potential, causing transistors 17?, 172, and 174 to be `cut od, and leaving relay 54 deenergized. When a timing signal appears across the resistor 164-, indicating that an item is incorrectly located on the transport means 114.- of the sorting apparatus, the transistor 19.65 will be cut off, and its collector voltage will approach the voltage of the potential source llt). The transistors 174i, 172, and 74 will be driven into conduction, causing the relay 54 to be energized for a time determined by the time constant of the resistor 175 and the capacitor 138, and thus for a time required by the relay S4 to open the switch element 42 of the main power circuit.

While the specific embodiment of the invention which is shown and described herein is admirably adapted to fulfill the objects primarily stated, it is to be understood that it is not intended to confine the invention to the one form or embodiment disclosed herein, for it is susceptible of embodiment in various other forms, all corning Within the scope and intent of the invention.

What is claimed is:

l. In apparatus operable with substantially opaque items, the combination of transport means defining a path of travel for said items; feed means for feeding said items to said transport means; timing means associated with said feed means for developing timing signals occurring in synchronism with operation of said feed means; control means comprising a plurality of photosensitive devices connected in series, and positioned at predetermined points adjacent to said path of travel; and means for applying light to said photosensitive devices including a light source for each of said photosensitive devices; said control means being responsive to said timing signals to effect control of said feed means when an item is adjacent to at least one of said predetermined points along said path of travel at a time coincidental with occurrence of a timing signal.

2. In apparatus operable with substantially opaque items, the combination of transport means defining a path of travel for said items; feed means for feeding said items to said transport means; timing means associated with said feed means for developing timing signals occurring in synchronism with operation of said feed means; means operable to prevent said feed means from feeding said items to said transport means; control means comprising a plurality of photosensitive devices connected in series, and positioned at predetermined points adjacent to said path of travel; and means for applying light to said photosensitive devices including a light source for each of said photosensitive devices; said control means being responsive to said timing signals to cause operation of said feed preventing means when an item is adjacent to at least one of said predetermined points along said path of travel at a time coincidental with occurrence of a timing signal.

3. In apparatus operable with substantially opaque items, the combination of transport means defining a path of travel for said items; feed means for feeding said items to said transport means; a source of operating potential connected to said feed means and said transport means; timing means associated with said feed means for developing timing signals occurring in synchronism with operation of said feed means; means operable to disconnect said feed means and said transport means from said source of operating potential; control means comprising a plurality of photosensitive devices connected in series, and positioned adjacent to said path of travel at predetermined points; and means for applying light to said photosensitive devices including a light source for each of said photosensitive devices; said control means being responsive to said timing signals to cause operation of said disconnecting means when an item is adjacent to at least one of said predetermined points along said path of travel at a time coincidental with occurrence of a timing signal.

4. In apparatus operable with substantially opaque items, the combination of transport means defining a path of travel for said items; feed means for feeding said items to said transport means; timing means associated with said feed means for developing timing signals occurring in synchronism with operation of said feed means; means operable by timing signals to prevent said feed means from feeding said items to said transport means; a gating circuit for passing timing signals to said feed preventing means; a plurality of photosensitive devices connected in series, and positioned at predetermined points adjacent to said path of travel; and means for applying light to said photosensitive devices including a light source for each of said photosensitive devices; said photosensitive devices being operable when an item is adjacent to at least one of said predetermined points along said path of travel to cause said gating circuit to pass a timing signal to said feed preventing means.

5. In apparatus operable with substantially opaque items, the combination of transport means defining a path of travel for said items; feed means for feeding said items to said transport means; timing means associated with said feed means for developing timing signals occurring in synchronism with operation of said feed means; means operable by timing signals to prevent said feed means for feeding said items to said transport means; a gating circuit for passing timing signals to said feed preventing means; current-responsive means having an input circuit and an output circuit, with the output circuit of said current-responsive means being connected to said gating circuit; a plurality of photosensitive devices having output electrodes coupled in series with said input circuit of said current-responsive means, said photosensitive devices being positioned at predetermined points adjacent to said path of travel; and means for applying light to said photosensitive devices to cause a first current to appear at said input circuit of said current-responsive means, said means for applying light to said photosensitive devices including a light source for each of said photosensitive devices; said current-responsive means being responsive to said first current to control said gating circuit in a manner to inhibit the passing of timing signals to said feed preventing means; each of said photosensitive devices being operable when an item prevents light from being applied thereto to cause a second current to appear at said input circuit of said current-responsive means; said current-responsive means being responsive to said second current to control said gating circuit in a manner to allow passing of a timing signal to said feed preventing means.

6. In apparatus operable with substantially opaque items, the combination of transport means defining a path of travel for said items; feed means for feeding said items to said transport means; timing means associated with said feed means for developing timing signals occurring in synchronism with operation of said feed means; means operable by timing signals to prevent said feed means for feeding said items to said transport means; a gating circuit for passing timing signals to said feedpreventing means; current-responsive means having an input circuit and an output circuit, with the output circuit of said current-responsive means being connected to said gating circuit; a source of voltage connected to said output circuit of said current-responsive means; a plurality of photosensitive devices having output electrodes coupled in series with said input circuit of said current-responsive means, said photosensitive devices being positioned at predetermined points adjacent to said path of travel; and means for applying light to said photosensitive devices to cause a first current to appear at said input circuit of said current-responsive means; said means for applying light to said photosensitive devices including a light source for each of said photosensitive devices; said current-responsive means being responsive to said first current to allow substantially the entire voltage of said source of voltage to be presented to said gating circuit thereby inhibiting the passing of timing signals to said feed-preventing means; each of said photosensitive devices being operable when an item prevents light from being applied thereto to cause a second current to appear at said input circuit of said current-responsive means; said current-responsive means being responsive to said second current to overcome the inhibiting effect of the voltage from said source of voltage on said gating circuit whereby a timing signal is passed by said gating circuit to said feed-preventing means.

7. In apparatus operable with substantially opaque items, the combination of transport means defining a path of travel for said items; feed means for feeding said items to said transport means; timing means associated With said feed means for developing timing signals occurring in synchronism with operation of said feed means; means operable by timing signals to prevent said feed means from feeding said items to said transport means; a gating circuit for passing timing signals to said feed-preventing means; current-responsive means comprising a first and a second signal-translating device, said current-responsive means having an input circuit and an output circuit, with the output circuit of said current-responsive means being connected to said gating circuit; a source of voltage connected to said output circuit of said current-responsive means; a plurality of photosensitive devices having output electrodes coupled in series with said input circuit of said current-responsive means, said photosensitive devices being positioned at predetermined points adjacent to said path of travel; and means for applying light to said photosensitive devices to make them conductive and cause a first current to appear at said input circuit of said currentresponsive means, said means for applying light to said photosensitive devices including a light source for each of s-aid photosensitive devices; said first current causing said first signal-translating device to conduct and said second signal-translating device to be cut off, whereby said current-responsive means operates to allow substantially the entire voltage of said source of voltage to be presented to said gating circuit, thereby inhibiting the passing of timing signals to said feed-preventing means;

each of said photosensitive devices being operable when an item prevents light from being applied thereto to cause a second current to appear at said input circuit of said current-responsive means; said second current causing said first signal-translating device to be cut off and said second signal-translating device to conduct whereby said current-responsive means operates to overcome the inhibiting effect of the voltage from said source of voltage on said gating circuit whereby a timing signal is passed by said gating circuit to said feed-preventnig means.

8. In apparatus operable with substantially opaque items, the combination of transport means defining a path of travel for said items; feed means for feeding said items to said transport means; timing means associated with said feed means for developing timing signals occuring in synchronism with operation of said feed means; means operable by timing signals to prevent said feed means from feeding said items to said transport means; a gating circuit for passing timing signals to said feedpreventing means; current-responsive means comprising a first and a second signal-translating device, said currentresponsive means having an input circuit and an output circuit, with the output circuit of said current-responsive means being connected to said gating circuit; a plurality of photosensitive devices having output electrodes coupled in series with said input circuit of said current-responsive means, said photosensitive devices being positioned at predetermined points adjacent to said path of travel; and means for applying light to said photosensitive devices to make them conductive and cause a first current to appear at said input circuit of said current-responsive means, said means for applying light to said photosensitive devices including a light source for each of said photosensitive devices; said first current causing said first signal-translating device to conduct and said second signal-translating device to be cut off, whereby said current-responsive means operates to control said gating circuit in a manner to inhibit the passing of timing signals to said feedpreventing means; each of said photosensitive devices being operable when an item prevents light from being applied thereto to cause a second current to appear at said input circuit of said current-responsive means; said second current causing said first signal-translating device to be cut off and said second signal-translating device to conduct, whereby said current-responsive means operates to control said gating circuit in a manner to allow the passing of a timing signal to said feed-preventing means.

References Cited in the le of this patent UNITED STATES PATENTS 2,171,362 Gulliksen Aug. 29, 1939 2,387,952 Smith Oct. 30, 1945 2,551,364 Coakley May 1, 1951 

